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@c This file is part of the GNU Dico manual.
@c Copyright (C) 2012-2019 Sergey Poznyakoff
@c This file is distributed under GFDL 1.1 or any later version
@c published by the Free Software Foundation.
This appendix summarizes search strategies available for use in Dico
@value{VERSION}.
@table @asis
@item exact
@cindex exact, a strategy
Match words exactly. This is a built-in strategy.
@item prefix
@cindex prefix, a strategy
Match word prefixes. This is a built-in strategy.
@item nprefix
@cindex nprefix, a strategy
This strategy is similar to @samp{prefix}, except that it allows the
user to limit the number of returned matches. If the search term has
the structure @samp{@var{skip}#@var{count}#@var{string}}, where @var{skip}
and @var{count} are integer numbers, then the @samp{nprefix} strategy
will return at most @var{count} headwords that begin with
@var{string}, omitting first @var{skip} unique matches.
This strategy is implemented in the @file{nprefix} loadable module.
@xref{nprefix}.
@item suffix
@cindex suffix, a strategy
Match word suffixes. This is a built-in strategy.
@item soundex
@cindex soundex, a strategy
Match words using SOUNDEX algorithm@footnote{See
@uref{http://en.wikipedia.org/wiki/Soundex}}. This strategy matches
headwords that sound approximately the same as the search term.
Note, that it is suitable only for English words.
This is a built-in strategy.
@item lev
@cindex lev, a strategy
Match headwords within given Levenshtein distance (1 by default).
This strategy accounts for the most usual spelling errors.
@cindex distance, Levenshtein
@cindex Levenshtein distance
The Levenshtein distance between two strings is the minimum number of
@dfn{edits} needed to transform one string into the other. The
edits are: insertion, deletion, or substitution of a single character.
Thus, Levenshtein distance 1 means that only one such operation
suffices to convert one string to another. This is the default for
that strategy.
This built-in strategy is used as a default one (@pxref{default
strategy}), unless the @code{default-strategy} configuration statement
mandates otherwise.
The dictionary server may optionally allow users to alter the
Levenshtein distance using the extension command @code{XLEV}. This
command is enabled by setting the @samp{xlev} capability.
@xref{Capabilities, xlev}, for a detailed description.
@item nlev
@cindex nlev, a strategy
Match normalized headwords within given Levenshtein distance. This
strategy is similar to @samp{lev}, except that it treats any runlength
of whitespace characters appearing in a headword as a single space
(ASCII 32) character.
@item dlev
@cindex dlev, a strategy
Match headwords within given Damerau-Levenshtein distance (1 by
default).
The Damerau-Levenshtein distance extends the Levenshtein distance by
an additional edit operation: transposition of two adjacent
characters.
This strategy is similar to @samp{lev}, but covers a much wider range of
spelling and typographical errors.
The distance threshold optionally be configured using the @code{XLEV}
command (@pxref{Capabilities, xlev}).
@item ndlev
@cindex ndlev, a strategy
This is the same as @samp{dlev}, except that it treats any runlength
of whitespace characters appearing in a headword as a single space
(ASCII 32) character.
@item re
@cindex re, a strategy
Match using POSIX 1003.2 regular expressions. This strategy treats
the search term as a regular expression (@pxref{Extended
regexps, Extended regular expressions, Extended regular expressions,
sed, GNU sed}).
@item regexp
@cindex regexp, a strategy
Match using basic regular expressions.
@item pcre
@cindex pcre, a strategy
Match using Perl-compatible regular expressions. This strategy is
implemented in the loadable module @file{pcre}. @xref{pcre}.
@item all
@cindex all, a strategy
Match everything. This experimental strategy ignores its argument and
matches all headwords. It is implemented in the @file{stratall}
module, which you must load if you wish to make that strategy
available. @xref{stratall}.
@item substr
@cindex substr, a strategy
Match a substring anywhere in the headword. This strategy is
implemented as a loadable module. @xref{substr}.
@item word
@cindex word, a strategy
Match a word anywhere in the headword. This is one of the strategies
provided by the @file{word} loadable module. @xref{word}.
@item first
@cindex first, a strategy
Match the first word within headwords. This strategy is
implemented in @file{word} loadable module. @xref{word}.
@item last
@cindex last, a strategy
Match the last word within headwords. This strategy is
implemented in @file{word} loadable module. @xref{word}.
@end table
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